Carrot leaf blights
Fungi (Alternaria dauci and Cercospora carotae), often together
| Type | Fungus |
|---|---|
| Cause | Fungi (Alternaria dauci and Cercospora carotae), often together |
| When | Midsummer to fall; Cercospora can show earlier, on young plants. |
About
Two common fungal blights that brown and kill carrot tops. The roots aren't infected, but weak tops mean smaller carrots and leaves that snap off when you pull.
Also called carrot leaf blight, Alternaria leaf blight of carrot, Cercospora leaf blight, leaf blights
How to recognize it
Symptoms
Alternaria makes irregular dark brown to black spots, mostly on edges and tips of older, lower leaves, and in warm wet weather whole beds can look frost-burned. Cercospora makes small flecks that become round tan or gray spots with dark edges, and it hits younger leaves early in the season. Spots on leaf stems can girdle them and kill the whole leaf.
Often confused with
Bacterial leaf blight looks similar, but its spots are angular, stay between veins, and run along the main veins with yellow, water-soaked edges.
Worse when
Long periods of wet leaves (8 to 12 hours or more) in mild to warm weather, about 61 to 86°F.
How it spreads
Comes in on seed; survives up to 2 years in carrot debris and on wild carrot (Queen Anne's lace), and spreads by wind and splashing water.
When
Midsummer to fall; Cercospora can show earlier, on young plants.
What to do, gentlest first
Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.
Resistant varieties and clean seed Prevent
Bolero resists both blights (and bacterial blight). Apache, SugarSnax 54, Sweet Bites, Nevis and others are also listed as tolerant. Buy seed from a reputable dealer.
Rotate and let leaves dry Prevent
Keep carrots out of that spot for 2 to 3 years, water early in the day, choose well-drained soil, and pull nearby Queen Anne's lace.
Clean up tops after harvest By hand
Remove or work in carrot tops and debris right after harvest so they break down fast.
Copper Organic spray
Wisconsin notes backyard growers can use copper-based fungicides, starting when spots first show up on leaves or leaf stems.
Copper protects new growth but doesn't cure spots. Follow the label, including days to harvest.
Plants it affects
Sources
Planting dates and advice are general guidance; check with your local Cooperative Extension office for your area.